The overall objective of this project is to increase our understanding of the interaction of ultrasound with tissue. Two complementary approaches are taken: (a) Studies of the acoustical properties of tissues to show the effects of tissue on sound propagation, and (b) Tests of physical mechanisms potentially responsible for the effects of ultrasound on tissues. The former are needed for an understanding of the latter. Our specific goals for the coming year include studies of (1) the absorption of sound in macromolecular solutions, bacteria and tissues, both normal and malignant, (2) nonlinear phenomena in the propagation of sound in tissues, (3) the effects of ultrasound on Drosophila, and (4) ultrasonic heating of tissues.